The present invention relates generally to semiconductor devices, and more particularly to metal-oxide-semiconductor field-effect transistors and related integrated circuit manufacturing techniques.
Prior art integrated circuit manufacturing techniques have employed silicon dioxide deposition in a number of areas, and particularly for purposes of masking silicon nitride. Formation of an oxide mask is typically achieved by selective etching using a photoresist mask of the same pattern desired for the oxide mask. Deposited silicon dioxide tends to contain hard particles, which makes it difficult to duplicate the good mask definition of the photoresist in the oxide. When a large number of silicon wafers undergo simultaneous silicon dioxide deposition, variations in thickness occur from wafer to wafer. Such variations necessitate an etch duration long enough to cut through the thickest oxide anticipated, which causes over etching of thinner oxide layers and consequently undesirable undercutting of the photoresist. Compounding such problems is the relatively fast etch rate of deposited silicon dioxide (compared to grown oxide, for example) which makes controlling the etch more difficult.
These and other problems of the prior art are eliminated or alleviated to a large degree by the present invention.